CVE-2013-0776 in Firefox
Summary
by MITRE
Mozilla Firefox before 19.0, Firefox ESR 17.x before 17.0.3, Thunderbird before 17.0.3, Thunderbird ESR 17.x before 17.0.3, and SeaMonkey before 2.16 allow man-in-the-middle attackers to spoof the address bar by operating a proxy server that provides a 407 HTTP status code accompanied by web script, as demonstrated by a phishing attack on an HTTPS site.
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Analysis
by VulDB Data Team • 05/05/2021
This vulnerability in Mozilla Firefox and related applications represents a significant security flaw that undermines the integrity of secure web communications. The issue affects versions prior to 19.0 for Firefox, 17.0.3 for Firefox ESR, 17.0.3 for Thunderbird, 17.0.3 for Thunderbird ESR, and 2.16 for SeaMonkey. The vulnerability stems from how these applications handle HTTP 407 status codes in proxy server environments, creating a pathway for sophisticated man-in-the-middle attacks that can deceive users about the authenticity of websites they are visiting.
The technical flaw manifests when a malicious proxy server responds to HTTPS requests with a 407 status code combined with embedded web script. This specific combination allows attackers to manipulate the browser's address bar display, making it appear as though users are visiting legitimate secure websites when they are actually communicating with attacker-controlled infrastructure. The vulnerability exploits the trust relationship between browsers and proxy servers, particularly when authentication is required for proxy access. This attack vector is especially dangerous because it operates at the application layer, bypassing traditional certificate validation mechanisms that users typically rely upon for secure browsing.
The operational impact of this vulnerability extends beyond simple phishing attacks, as it enables sophisticated social engineering campaigns that can deceive even security-aware users. Attackers can leverage this flaw to conduct credential theft operations, data exfiltration, and other malicious activities while maintaining the appearance of legitimate secure connections. The vulnerability is particularly concerning for enterprise environments where proxy servers are commonly deployed, as it can be used to target employees accessing corporate resources through authenticated proxy configurations. This flaw directly relates to CWE-345 Insufficient Verification of Data Authenticity, which addresses the failure to properly validate data integrity in security-critical operations.
Security professionals should recognize this vulnerability as a potential target for advanced persistent threat campaigns that exploit trust relationships in network infrastructure. The attack methodology aligns with techniques described in the ATT&CK framework under T1071.004 Application Layer Protocol: DNS and T1566 Phishing, as it combines network-level manipulation with social engineering to compromise user trust. Organizations using affected software versions should prioritize immediate patching of all affected applications, including Firefox, Thunderbird, and SeaMonkey, to prevent exploitation. Additionally, network administrators should review proxy server configurations and implement additional monitoring for unusual 407 responses that could indicate attempted exploitation of this vulnerability.
The remediation approach requires updating to patched versions of all affected software components, as the vulnerability cannot be effectively mitigated through configuration changes alone. Security teams should implement network monitoring to detect potential exploitation attempts and establish incident response procedures for identifying and containing attacks that leverage this flaw. The vulnerability demonstrates the importance of comprehensive security testing that includes proxy server interactions and authentication flows, as these scenarios can create unexpected attack vectors that bypass traditional security controls. Organizations should also consider implementing additional layers of authentication and verification for critical applications to reduce the impact of such vulnerabilities when they occur.